The present invention relates to a rotary control valve with a variable area orifice that communicates with a bypass channel when the valve is in the less than full-open position. This arrangement effectively eliminates cavitation and noise in the valve when not in the full-open position. More specifically, the invention relates to a rotary control valve with a variable area orifice in the control element that communicates with a bypass channel in the less than full-open position. Variable area rotary control valves are already widely used in the petroleum refining and chemical industries. Several types of these valves with rotary control elements have been patented, including the following patents:
U.S. Pat. No. 3,443,793 PA1 U.S. Pat. No. 3,558,100 PA1 U.S. Pat. No. 3,612,102 PA1 U.S. Pat. No. 4,212,321 (the "Hulsey 321 Patent").
The present invention may be described as an improvement over the present state-of-the-art valves which are used to control flow velocity and pressure drop of fluids or gases through various flow conduits. The current state of the art technology uses rotary-type valves, which, when rotated through predetermined degrees of rotations, provide a controlled variation of the flow path from the full open position to the complete shut-off position. The full-open position provides maximum flow with variable flow decreasing to the complete shut-off position.
In addition to controlling the flow characteristics (i.e., velocity and pressure), the rotary valves currently used often contain a noise-reduction means to suppress the noise inherently created with the restriction of the high velocity flow of fluids and gases through a rotary control valve. These noise suppression means in the prior art consist primarily of diverting the through-flow through a labyrinth of multiple flow-ways creating a tortuous flow-path that therefrom creates a restricted flow coupled with a dissipation of energy, resulting in substantially reduced noise levels.
The Hulsey '321 patent provides such a means to vary a flow path using two opposed divergent spiral grooves, one of which is in register with the upstream port and the other of which is in register with the downstream port. When the spiral grooves are rotated in the flow-path, flow is diverted into a tortuous path thereby creating a controlled restriction of flow and noise suppression. When the flow-control means in the Hulsey '321 patent is in the full-open position, the valve provides a non-restricted flow-path. The Hulsey '321 patent also describes a valve whereby noise is further reduced by placing other noise-silencing means within the flow-control member of the valve as well as within the two opposed divergent spiral grooves.
The noise suppression means described above present several difficulties. Primarily, the noise suppression means currently referred to in the prior art are subject to wear, erosion, and clogging. As such, valves employing these flow control and noise suppression means require substantial maintenance. Maintenance often times requires replacement of the control member or the noise-silencing means. At a minimum, because the design of the rotary valves described in the prior art precludes the design of a top-entry valve body, maintenance to such a valve requires that the valve be completely removed from the line, disassembled, retrimmed and then reinstalled at considerable expense.